Download Soil carbon accounting - Forestry and Agriculture Greenhouse Gas

Soil carbon accounting:
options to measure, monitor, and
address project-level issues
Forestry & Agriculture Greenhouse Gas Modeling Forum
Shepherdstown, West Virginia
8-11 October 2002
Tris West
Environmental Sciences Division
Oak Ridge National Laboratory
OAK RIDGE NATIONAL LABORATORY
U.S. DEPARTMENT OF ENERGY
Potential trade-offs between environmental
integrity and economic incentives
Issues that may arise in
efforts to maintain
environmental integrity
 What is accuracy of soil C
measurements or estimates?
 Are changes in land use and
climate considered?
 Are other environmental
effects (e.g., changes in GHG
emissions) considered?
 Additionality, permanence,
saturation, & leakage
 Consider simplicity & flexibility
Issues that may arise if
incentives for C
sequestration are provided
 What level of accuracy is
desired?
 What are acceptable amounts of
time and costs associated with
measuring and monitoring?
 What are acceptable levels of
economic risk (e.g., risk of not
meeting sequestration
obligation)?
 Who is eligible for incentives
(targeting)?
 Consider simplicity & flexibility
Focus: soil C changes in agricultural soils
Conventional Tillage
(CT)
No-Till
(NT)
Photos courtesy of Donald Tyler, Univ. of TN, West TN Ag. Exp. Station
Presentation outline
I.
Current options for measuring and monitoring
A. Summary of measurement options
B. Issues associated with measurement options
C. Discussion of carbon management response curves
1. Project-level issues
2. Accounting for other greenhouse gases
II.
Comparison of options
III. Conclusions
Option 1: Measuring soil carbon change
 Ex situ – soil sampling (analyzed in lab)
 In situ – soil sampling (analyzed in field)
 Laser Induced Breakdown Spectroscopy
(Cremers et al. 2001, Martin et al. 2002)
 Surface-Enhanced Raman Scattering
(Stokes & Vo-Dinh 2001)
 Inelastic Neutron Scattering
(Wielopolski et al. 2000)
 Eddy Covariance – net ecosystem exchange
Option 2: Estimating soil carbon change
 Remote sensing capabilities
 Process models
 Database accounting
See also:
Post et al. 2001. Monitoring and verifying
changes of organic carbon in soil.
Climatic Change 51:73-99.
Option 3: Incentive based on practice
Approach similar to Conservation Reserve Program:
 Payments for cropland “set aside” for a fixed time period.
 Decreases in soil erosion are not measured.
Carbon accounting issues related to carbon
measurements (Option 1)
 Is it reasonable to provide an incentive based on
natural variability of soil carbon measurements?
 How do we know when soil C has reached
saturation or a new equilibrium?
 Do we know that all change in soil C is due to the
change in practice (is there a control plot or
baseline estimate)?
Cumulative C sequestered in soil
with a change from conventional
tillage to no-till (g m-2)
Example: Comparison between measured and
estimated changes in soil carbon
2500
95% C.I.
2000
1500
1000
Estimated mean
change in soil C
from West & Post
(2002). SSSAJ
66:1930-1946.
500
0
0
10
20
Time (year)
Measured change in soil C (in red)
Illinois corn/soybean (Kitur et al. 1994)
30
40
Cumualtive C sequestered in
soil with a change from
conventionall tillage to no-till
(g m-2)
Example: Comparison between measured and
estimated changes in soil carbon
95% C.I.
1400
1200
1000
800
600
400
200
0
-200
-400
Estimated mean
change in soil C
from West & Post
(2002). SSSAJ
66:1930-1946.
0
10
20
Time (year)
Measured change in soil C (in red)
Kentucky continuous corn (Ismail et al. 1994)
30
40
Example: Comparison between measured and
estimated changes in soil carbon
2500
Ohio corn/soybean rotation
Cumulative C sequestered in soil with a
change from conventional tillage to no-till
(g m-2)
2000
1500
Estimated mean change in
soil C from West & Post
(2002). SSSAJ 66: 19301946.
1000
500
0
1400
Ohio continuous corn
1200
1000
Measured change in soil C
(in red) Dick et al. (1997)
800
600
400
200
0
0
10
20
Time (year)
30
40
Changes in soil carbon due to climate suggest
the need to consider issues of additionality and
saturation
Campbell et al. 2001. Canadian Journal of Soil Science 81:383-394.
Introducing Option 4
Option 1: Measuring soil carbon change
Option 2: Estimating soil carbon change
Option 3: Incentive based on practice
Option 4: Estimate change in C based on
practice using average measured responses
Approach is a hybrid between options 1, 2 and 3:
 Development of Carbon Management Response Curves
Carbon Management Response Curves —
carbon accumulation under no-till
Average annual C sequestration
rate following a change from
CT to NT (%/yr)
Uncertainty
1.4
1.2
Mean
95% C.I.
1
0.8
0.6
Mean
sequestration
and duration
0.4
0.2
0
0
10
20
Time (years)
30
40
Targeting
Estimate: 11 ± 2% (normalized to original land use)
Source: West & Post (2002). Soil Sci. Society of Am. J. 66:1930-1946
Carbon Management Response Curves —
Average annual C sequestration
rate following a change from
cultivated land to forest (%/yr)
carbon accumulation following afforestation
2.5
Mean
95% C.I.
2
1.5
1
0.5
0
0
10
20
30
40
50
60
Time (years)
Estimate: 37±12% (normalized to original land use)
Sources: Gao & Gifford (2002), Paul et al. (2002), Post & Kwon (2000)
Carbon Management Response Curves —
Average annual loss of soil C
following cultivation of forested
land (%/yr)
soil carbon loss following cultivation
0
-2
-4
-6
-8
-10
-12
-14
0
5
10
15
20
Years in cultivation
Estimate: -30 ± 5% (normalized to original land use)
Sources: Mann 1986, Post & Mann 1990, Davidson & Ackerman 1993, Murty et al. 2002
Carbon Management Response Curves —
Integrating changes in land use
“…there are not enough data available to perform a
meta analysis of the land use change from pasture
or forest to no-tillage crop.”
- Guo & Gifford (2002)
12
10
8
6
4
2
0
-2
-4
Scenario: Deforest, cultivate with CT for 20
yr, change to NT for 10 yr, use CT for 1 year,
change back to NT for 10 yr, reforest at year
50.
Conventional
tillage
Deforestation
(CT)
No-till
No-till (NT)
Afforestation
Forest
Average cumulative C
flux to the atmosphere
(%)
Average annual rate of C
flux to the atmosphere (%/yr)
Estimating carbon stocks following changes
in land management using CMR curves
12
10
8
6
4
2
0
-2
-4
40
30
20
10
0
-10
0
20
40
60
80
100
Years
0
20
40
60
80
100
Permanence
Years
Change in soil C with change in land use
Integration over time
Estimating changes in GHG emissions associated
with soil C sequestration using CMR curves
Accounting of changes in GHG emissions assumes:
• Soil C sequestration of 570 ± 140 kg C/ha/yr [normal distribution]
• Average US production inputs and associated emissions
• Estimated relationship between N fertilizer and N2O
emissions of 2.66 kg Ceq / kg N applied (2% of N applied)
• Potential change in N2O emissions of 7 ± 15% with
change from CT to NT [uniform distribution]
• Potential change in yield of ± 6% [uniform distribution]
• Change in cropped area that ranges from full compensation for
the change in crop yield to no response to the change in yield
[uniform distribution]
Cumulative change in SOC and
CO2 and N2O emissions to the
atmosphere (kg/ha)
Savings in CO2 and N2O emissions are permanent while
C sequestered in soil may be temporary
Change in N2O emissions
Change in SOC
Change in CO2 emissions
4000
2000
Permanent
0
-2000
-4000
-6000
Temporary
-8000
0
10
20
30
Time (year)
40
50
Emissions that are released as a result of an implemented
carbon sequestration strategy may represent a future
liability
Cumulative change in net GHG flux
to the atmosphere (kg/ha)
Change in SOC, CO2, and N2O
Change in SOC
Change in SOC and CO2
Credit
Liability
0
-2000
-4000
-6000
Temporary
-8000
-10000
0
10
20
30
Time (year)
40
50
Permanent
Carbon management response curves — Summary
Upon further development, CMR curves may effectively
address:
•
•
•
•
•
•
•
•
Integration of practices over time
Duration of C sequestration rates (saturation)
Uncertainty in C sequestration rates
Additionality (cancels out climate effect)
Possible inclusion of net carbon/GHG accounting
Targeting
Permanence
Temporal and spatial variability
A general and qualitative comparison of some options
to measure/estimate changes in soil C stocks
Cost of
Accuracy Account for Risk of not
Simplicity
Measuring & of change saturation or meeting seq. and flexibility
monitoring in C stock seq. duration obligation of accounting
Direct
(in situ)
Medium
High 
LowMedium
MediumHigh
Low-Medium
Direct
(ex situ)
High
High 
LowMedium
MediumHigh
Low-Medium
Practice
Low

Low
Low
Low

High

Hybrid
(avg.
estimate)
Low

Medium
High
Low

High


Concluding remarks
 Options to measure & monitor partly depend on ability
to address project-level issues
 Costs, simplicity, predictability, flexibility, as well as
saturation, additionality, and permanence all appear to
be more effectively addressed by the use of average
sequestration or loss rates (CMR curves) rather than
direct C measurements
 In addition, CMR curves allow for integration of several
practices over time and possible inclusion of net GHG
accounting
 Similar comparison could be done with economic/
incentive options and combined with measuring &
monitoring options to develop a comprehensive
carbon accounting framework
Acknowledgments
OAK RIDGE NATIONAL LABORATORY
U.S. DEPARTMENT OF ENERGY
Consortium for Research on Enhancing
Carbon Sequestration in Terrestrial Ecosystems